In recent years, various electronic devices taking advantage of properties, e.g., hysteresis, a pyroelectric effect, a piezoelectric effect, and an electrooptical effect, exhibited by a ferroelectric have been researched. Most of all, an application of a device including a Metal/Ferroelectric/Metal/Insulator/Semiconductor (MFMIS) structure to nonvolatile memory elements and sensors is expected.
As for this structure, it is expected that the device performance can be improved and the size can be miniaturized by making the ferroelectric a thin film. Furthermore, it is believed that integration with an integrated circuit can be performed by using a semiconductor substrate.
In the device including the MFMIS structure, an upper electrode and a lower electrode are necessary to derive a signal from the ferroelectric or give a signal to the ferroelectric. For example, in the case where the ferroelectric is used as a sensor, signals appear at the upper and lower electrodes due to a physical effect applied to the ferroelectric. In the case where the ferroelectric is used as a memory element, electric signals must be given from the upper and lower electrodes to the ferroelectric in accordance with the data to be stored.
On the other hand, the crystallinity of the ferroelectric is an important factor that determine the performance of the device. Since the ferroelectric is formed on a metal electrode in the MFMIS structure, the electrode is also required to have good crystallinity. Platinum (Pt) is used widely as a metal material for electrode at present.
In the field of sensor devices, Pb(Zr,Ti)O3 (PZT) base ferroelectric materials are used widely. It is known that the PZT base materials exhibit best ferroelectric properties when the crystal faces on the electrode are made to be (001) faces uniformly. In order to attain the PZT(001), Pt of the lower electrode must be a single crystal in which the (001) faces are aligned, and a single crystal MgO(001) substrate is used at present to attain such Pt. A Pt(111) oriented film and a PZT(111) oriented film thereon can be produced by using a substrate in which a silicon (Si) oxide film is formed on the surface of a silicon (Si) substrate and, thereafter titanium is deposited.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2002-261249 (pages 4 to 5, FIG. 2)
[Non-Patent Document 1]
Akai et al., Extended Abstracts (the 49th Meeting), the Japan Society of Applied Physics and Related Societies, 30a-ZA-6